Cellular organic rigid thermosetting plastic foams used for thermal insulation are well know in the art. Such foams can be made with urethane linkages, or made with a combination of both isocyanurate linkages and urethane linkages, or they can be made via the well known condensation reaction of formaldehyde with phenol, urea, and melamine. All such plastic foams must utilize an expansion agent, often referred to as a "blowing agent."
The prior art is replete with references to techniques of expanding foam cells. For many years, the dominant blowing agent for all thermosetting foams was trichloromonofluoromethane (CFC-11). Hydrogenated chlorofluorocarbons (HCFC's) are considered to be environmentally friendly expansion agents, but still contain some chlorine, and therefore have an "Ozone Depletion Potential" (ODP). Because of the ODP, the HCFC's have been mandated for eventual phase-out.
Hydrocarbon blowing agents are also known, which class includes halogen-free and CO.sub.2 -free blowing agents. For example, U.S. Pat. No. 5,182,309 (Hutzen) teaches the use of iso- and normal-pentane in various emulsion mixtures. Another example of hydrocarbon blowing agents is taught in U.S. Pat. No. 5,096,933 (Volkert), pointing out the virtues of commercial cyclopentane distilled and extracted from natural gas wells.
Accordingly, cyclopentane is expected to replace ozone-depleting halogen-containing compounds as the blowing agent for manufacturing of polyurethane foam insulation. The volatility and low thermal conductivity of cyclopentane make it uniquely suitable for this application.
One route for manufacturing cyclopentane involves recovery by distillation from naphtha streams derived from crude oil or field natural gasoline. Very limited quantities of cyclopentane can be produced via this route due to the low concentrations of naturally occurring cyclopentane. Furthermore, cyclopentane product purity via this route is limited to approximately 75% by the presence of 2,2-dimethyl butane (which has a boiling point less than 1.degree. F. (0.55.degree. C.) different from cyclopentane). Further purification requires more expensive processing such as extractive distillation.
Extracted cyclopentane has at least five problems which heretofore virtually prohibited it from being considered a serious candidate as a commercial blowing agent for rigid foam insulation. The first problem is that its limited supply is considerably below the amount needed to meet the quantity demanded of a commercial compound. The second problem is that this inadequate supply contains at least twenty-two percent impurities in the form of hexane isomers and n-pentane, which impurities significantly reduce insulating value of foam made therefrom. The third problem is that extracted cyclopentane is not miscible with the common polyester polyols which are used with HCFC'S, nor those that were used with CFC-11. The fourth problem is that extracted cyclopentane does not reduce the viscosity of the polyester polyol foamable blend to a workable level, even when liquid fire retardants are utilized.
The fifth problem is that the foam produced with extracted cyclopentane will not pass the ASTM E-84 maximum 75 Flame Spread Index even with moderate flame retardant.
Another possible route for manufacturing cyclopentane involves hydrogenation of cyclopentene; however, cyclopentene is not readily available in commercial quantities.
Another route to produce a high purity cyclopentane, and the subject of the present invention, involves splitting dicyclopentadiene (DCPD) into cyclopentadiene (CPD) monomer and hydrogenating the monomer to form cyclopentane. A key advantage of this route is an abundance of commercially available, low-cost DCPD raw material. Technical obstacles involve: (1) effective splitting of DCPD without forming heavy resins that diminish product yields and foul the splitting equipment; and (2) preventing unwanted reaction of the highly reactive monomer which decreases desired product yield, form unwanted by-products, and can lead to deactivation of the hydrotreating catalyst. Examples of such processes are set forth in GB-A-2271575 and GB-A-2273107, which are incorporated herein by reference and which are commonly assigned to the assignee of the present invention.
The present invention also provides many additional advantages which shall become apparent as described below.